Oil-hydraulic servo-motor

ABSTRACT

An oil-hydraulic servo-motor with a servo piston defining a high and a low oil pressure chamber in a cylindrical bore and control valve means adapted to place the high and low oil pressure chambers in communication with the output power cylinder under control of an input member. The servo piston forms together with the cylindrical bore a valve mechanism operable to place the high and low oil pressure chambers in communication with each other upon advancing movement of the servo piston beyond a definite axial position, rendering the servo-motor operable even in case of failure in the pressure oil system directly under the action of the input member. Any unpleasant impulsive reaction to the operator is avoided by the provision of an oil throttling orifice serving to prevent rapid build-up of oil pressure on the input piston. A spring-loaded relief valve inserted in the oil outlet line serves to keep all the spaces in the servo-motor filled with oil and enables it to respond to the input at all times without delay.

United States Patent 11 1 1111 3,

Nakagawa Dec. 16, 1975 OIL-HYDRAULIC SERVO-MOTOR Primary Examinerlrwin C. Cohen [75] Inventor: Tadao Nakagawa, Ueda Japan Attorney, Agent, or Flrm-Haselt1ne, Lake & Waters [73] Assignee: Nisshin Kogyo Kabushiki Kaisha,

Japan [57] ABSTRACT [22] Filed: June 6, 1974 An oil-hydraulic servo-motor with a servo piston defining a high and a low oil pressure chamber in a cylin- [Zl] Appl' 477064 drical bore and control valve means adapted to place the high and low oil pressure chambers in communica- [30] Foreign Application Priorit D t tion with the output power cylinder under control of Apr. 24, 1974 Japan 49-46177 an input member- The Servo Piston forms together with the cylindrical bore a valve mechanism operable 52 us. c1 91/391 R; 60/547; 91/434; to P e high e Pressure Chamber? in 91/450 communication with each other upon advancing 51 1111. C1 ..F15B 13/10 le of e Servo Piston beymd a definite axial [58] Field of Search 91/434, 391, 450; 60/547 Posmom f the Servo-motor opereble m case of fallure 1n the pressure Oil system directly under [56] References Cited the action the irt1tput menlber Any gtrziplaeastalnt impu s1ve reac ion 0 e opera or is avot e y e pro- UNITED STATES PATENTS vision of an oil throttling orifice serving to prevent i.708,l73 4/1929 Hansen 91/468 X rapid build up of n pressure on the input piston A g; 132; i 45 2 spring-loaded relief valve inserted in the oil outlet line 15667 12/1963 t [4 X serves to keep all the spaces in the servo-motor filled 3:126:794 3/1964 Ayers: 91/434 X wlth oil and enables it to respond to the input at all 3252,3212 5/l966 Kellogg et 111.. 91/434 Wlthout y- 3,526,089 9/1970 Fulmer 9l/434 X 3 Claims 3 Drawing Figures E 7 M P C I 4 20,112 l5 9 28 v m 1 36 I -3 R 3 a V l9 lB 4 US. Patent Dec. 16, 1975 OIL-HYDRAULIC SERVO-MOTOR BACKGROUND OF THE INVENTION This invention relates generally to servo-motors of the oil-hydraulic type operable under oil pressure supply from an appropriate source such as an oil pressure pump or an oil accumulator to actuate an automotive brake or like mechanism.

Previous forms of servo-motor of the type described have involved various difficulties as follows: First, any failure in the oil pressure system renders the device un able to function properly and impairs driving safety. Further, in normal operation, the operator is often subjected to an unpleasant impulsive reaction through the operating member particularly when he operates it suddenly, principally on account of the rapid flow of pressure oil into a reaction oil pressure chamber, which is defined in the servo-motor and in which oil pressure builds up as the output power cylinder is fed with pres sure oil from an appropriate source through control valve means with advancing movement of the input piston, associated with the operating member.

Another difficulty with previous forms of servomotor has been that the servo output is often delayed even when there is no trouble in the oil pressure system particularly in cases where the servo system has been left out of operation for some period of time. It has been found, however, that such delay in time of operation is due to the fact that during the time when the systemv is left inoperative empty spaces or hollows are formed therein particularly in the output power cylinder and the reaction oil pressure chamber as the oil left in such spaces flows out to the oil reservoir side thereof under gravity or on account of the expansion of vapor bubbles involved. Under such situation, the output power cylinder apparently cannot start to work until the hollows in the system are filled up under input operation.

SUMMARY OF THE INVENTION The present invention is intended to overcome such difficulties previously met with servo-motors of the type described and has for its principal object the pro vision of a new and improved oil-hydraulic servo-motor which not only normally gives an output adjustable with limited movement of the input member while enabling the operator to feel the intensity of such. output exactly through the input member and avoid any excessive input operation but is operable in any failure of the oil pressure system to actuate the associated device such as an automotive brake directly under the operators input effort and highly valuable from the standpoint of safety.

Another object of the present invention is to provide a servo-motor of the character described which is de signed so as to allow flow of pressure oil into the reaction oil pressure chamber only at such a limited rate as not causing any upleasant feeling to the operator even under sudden input operation.

Still another object of the present invention is to pro vide a servo-motor of the character described which is kept free from formation of any hollows in the power cylinder or the reaction oil pressure chamber even if the system is left inoperative for an extended period of time and thus can respond to the input as given by the operator at all times without delay.

These and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, which illustrates a preferred embodiment of the present invention as applied to an automotive brake system;

FIG. 1 represents a partly schematic, axial cross section of the embodiment;

FIG. 2 is a transverse cross-sectional view taken along the line IIII in FIG. 1; and

FIG. 3 is a view similar to FIG. 2, taken along the line IIIIII in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, reference character M indicates a well-known form of brake master cylinder, in which an operating piston 1 is accommodated to serve the purpose of supplying pressure oil to the oilhydraulic components of the brake system. Connected to 'the master cylinder M at its rear end is a power cylinder P to the rear of which a control casing C is .connected. An output piston 2 is slidably fitted in the power cylinder P and operably connected to the rear end of operating piston 1 with a restoring spring 3 arranged under compression between the master cylinder M and output piston 2 to bias the latter rearwards.

The control casing C has an interior space in the form of a shouldered cylindrical bore 4, which is in align ment with the power cylinder P and has a rear portion slightly reduced in diameter and connected with the forward, major bore portion through the medium of a tapered annular shoulder surface 5. A servo piston 6 is slidably fitted in the reduced-diameter portion of the cylindrical bore 4 and defines therein a high oil pressure chamber A and a low oil pressure chamber B respectively on the front and rear sides thereof. Extending axially forwardly from the servo piston 6 is an integral piston rod 6a which is slidably fitted in the rear portion of the power cylinder P- to serve as a stop for limiting the retracting movement of the output piston 2. As shown, the piston 6 is formed at its forward end with an integral annular flange 7, which is slidably fitted in the major or larger-diameter portion of the cylindrical bore 4 and is formed with a number of radial notches 7a at circumferentially equal intervals, as shown in FIG. 3.

Connected to the high oil pressure chamber A is a high pressure line L which is connected at the other end with an oil pressure pump 8 and includes an oil accumulator A low pressure line L is connected to the low oil pressure chamber B and opening at the other end into an oil reservoir 10. A relief valve 11 is arranged midway of the low pressure line L and adapted to open when the oil pressure in the low oil pressure chamber A reaches a predetermined level. Reference numeral 12 indicates a pressure-regulating spring arranged on the valve 11 and serving to restore it to its normal closed position.

The servo piston 6 is formed with a cylindrical axial bore 13 opening rearwardly to receive a stopper element 14, which defines a valve chamber 15 in the forward portion of the axial bore 13. The valve chamber 15 is in fluid communication with the high oil pressure chamber A through an oil inlet port 18 formed in the front wall of the valve chamber and further through an axial enlarged diameter bore 19 and transverse or diametral bores 20 all formed in the pistonrod 6a, as shown in FIG. 2. The valve chamber 15 is also incomted therein for limited axial displacement and a valvespring 17 normally biasing the valve element 16 rearwards. As shown, a ball-shaped second valve element 22 is accommodated in the axial bore 19 to close the oil inlet port 18 under the bias of a valve-closing spring 23 also accommodated in the axial bore 19. A valve-opening rod 24 is extended forwardly from the first valve element 16 so that the second valve element or ball 22 is pushed forward by the rod 24 to open the oil inlet port 18 when the first valve element 16 is advanced.

The stopper element 14 is formed therein with a cylindrical bore 26, which communicates with the valve chamber 15 by way of through apertures 25 formed in the first valve element 16 and an annular flange 27 ex-.

tends radially inwardly from the inner peripheral wall of the cylindricalbore 26 at a location adjacent to the forward end thereof. An input piston 28 is slidably fitted, in the cylindrical bore 26 and defines therein a re-.

action oil pressure chamber R in co-operation with the annular flange 27. .Formed on the front face of the operating piston 28 is an axial tubular projection 29 which extends into the annular flange 27 and defines together therewith an annular opening or orifice 30. An annular stop 31 is secured to the periphery of input piston 28 to limit rearward movement thereof by abutting engagement with the adjacent wall of the control casing C. A biasing spring 62 is arranged between the stop 31 and, stopper element 14 to normally hold the input piston 28 in its fully retracted position keeping a limited axial space between the first valve element 16 and tubular projection 29.

Formedin the input piston 28 is an axially extending oil outlet port 34 which openes forwardly through thetubular projection 29 and communicates at the rear end with the low oil pressure chamber B through a diametral bore or bores 33 formed in the input piston in intersecting-relation with the oil outlet port 34. It is to be understood that in this arrangement the oil outlet port 34 is closed against the back face of the first valve element 16 when the input piston 28 is driven forward.

An operating rod 36 is connected with the rear end of the input piston 28 by way of a cushioning member formed of rubber or the like material and, as will readily be understood, is operably connected with a brake pedal, not shown. Reference numeral 37cindicates annular seals fitted to the outer periphery of the servo piston 6 and other piston members of the servomotor.

In the drawing, the servo-motor is shown in it s inop erative position in which, as long as the oil pressure pump 8 and accumulator 9 are in normal operating condition, the high oil pressure chamber A is kept filled with pressure oil from the pressuresupply source so that the piston 6 is firmly held in its normal fully re tracted position, as shown, under the oil pressure.

is closed and subsequently the valve element 16 is driven forward to push forward the second valve ele ment 22 by means of the valve-opening rod 24 thereby to open the oil inlet port 18. As the consequence, the

power cylinder P is fed with pressure oil from the high oil pressure chamber A through the diametral bores 20,

axial bore 19 valve chamber 15 and oil passages 21 and the output piston 2 is driven forward together with the piston l in the master cylinder M thereby to energize the associated brake system.

On the other hand, part of the pressure oil flowing in the valve chamber 15 is directed through the annular orifice 30 into the reaction oil pressure chamber R and the oil pressure thus built therein acts upon the input piston 28 as a reaction against the input force applied by the operator. The force of reaction is in proportion to the oil pressure in the power cylinder P and the operator can tell the intensity of the output of piston 2 exactly by feeling the magnitude of such reaction. In addition, as the flow of pressure oil into the reaction oil pressure chamber R is properly throttled by the annular orifice 30, the rise in oil pressure in the chamber R is comparatively slow even where the pressure rise in thepower cylinder P is sudden and fast. This means that thereaction acting upon the input piston 28 is at all times never impulsive, giving no unpleasant feeling to th'e'operator. I

Subsequently when the brake pedal is released, the input piston 28 is restored to its rearmost position under the bias of restoring spring 32 and the two valve elements 16 and 22 operate reversely to close the oil inlet port 18 while opening the oil outlet port 34 to place the power cylinder P in fluid communication with the low oil pressure chamber B, thus allowing the outputpiston '2 to retract under the resilience of the restoringspring'3. Accordingly, the oil previously fed in the power cylinder P is led through oil passages 21, valve chamber 15, oil-outlet port 34 and diametral bores 33 into the/low oil pressure chamber B and, opening the relief valve 11, recirculates through the low pressure line L into the oil reservoir 10. On this occasion, it is to be noted that the relief valve 1 1 is reclosed under the bias of spring 12 at the instant when the oil pressure in the low oil pressure chamber B is reduced to a predetermined level to maintain such level of oil pressure in the low oil pressure chamber B and in the power cylinder P, valve chamber 15, reaction oil pressure chamber R- and other interior spaces communicating with the low oil pressure chamber B.

,In other words, whenever the servo-motor is restored to its inoperative state, the power cylinder P, valve chamber 15 and reaction oil pressure chamber R are left filled withoil under a predetermined level of pressureand no empty space is formed in the system. Accordingly, when subsequently an input force is applied to .the piston 28, the pressure oil held in the high oil count 'ofJ some failure in the oil pressure system includ- Now it is assumed that the brake pedal is stepped on v and the input piston 28 is driven forward. ln this event, first the axial projection 29 on the input piston 28 comes into abutting engagement with the back face of the first valve element 16 so that the oil outlet port 34 ing 'th'e oil pressure pump 8, accumulator 9 and high pressure line L. Y

' In such ases, the input piston 28 started as usual hefoperator' s' input effort and immediately d f f place'gljin 'iabutting engagement with the annular flange 27 on stopper element 14 acts to drive forward the servo piston 6 and piston rod 6a through the medium of stopper element 14 because of the lack of oil pressure serving to hold the servo piston 6 in its retracted position. In this manner, the piston l in the brake master cylinder M is actuated under the input in an effective manner despite of the failure in the oil supply system.

Again in such cases, when the servo piston 6 has advanced a certain distance, leaving the smaller diameter portion of cylindrical bore 4, the high and low oil pressure chambers A and B are placed in fluid communication with each other through notches 7a, formed in the annular flange 7 of servo piston 6 and through the smaller diameter bore portion. The oil held in the high oil pressure chamber A is thus allowed to flow into the low oil pressure chamber B as the servo piston 6 continues to advance and does not restrain its advancing movement to any extent. Further, the piston 6 is kept in axial alignment with the cylindrical bore 4 for smooth sliding movement without jolting even after it has left the smaller diameter portion of cylindrical bore 4 as the annular flange 7 formed on the piston 6 at its forward end is still held in sliding engagement with the peripheral wall of the larger diameter portion of cylindrical bore 4.

Upon removal of the input, the servo piston 6 is retracted together with the output piston 2 under the bias of restoring spring 3 to again fit into the smaller diameter portion of cylindrical bore 4 without any danger of being injured as the annular seal 37 slightly bulging radially around the periphery of the piston 6 is guided into the smaller diameter bore portion smoothly over the tapered annular shoulder surface 5 formed on the bore wall.

While it will be apparent that the preferred embodiment herein illustrated is well calculated to fulfil the objects stated above, it will be appreciated that the invention is susceptible of modification, variation and change without departing from the spirit of the invention or from the scope of the appended claims.

What is claimed is:

1. An oil-hydraulic servo-motor comprising: a power cylinder having a bore and an output piston slidably fitted in said bore, a control casing secured to said power cylinder at the rear end thereof and defining a cylindrical bore in axial alignment with said power cylinder, a servo piston slidably fitted in said cylindrical bore and defining, when fully retracted, a high and a low oil pressure chamber in said cylindrical bore, respectively, in the front and rear portions thereof, a piston rod extending axially and forwardly from said servo piston and held in sliding engagement with the rear end portion of said power cylinder in end-to-end relation with said output piston, an oil pressure supply source connected to said high oil pressure chamber, an oil reservoir communicatin g with said low oil pressure chamber, a reaction oil pressure chamber defined in said servo piston and communicating with the bore in said power cylinder, an input piston slidably supported in said control casing in axial alignment with said servo piston and having the piston face thereof extending forwardly into said reaction oil pressure chamber, and control valve means operable in response to limited forward and rearward movement of said input piston to place the bore in said power cylinder in and out of fluid communication with said high and low oil pressure chambers, said cylindrical bore of the control casing having a larger diameter front portion and a smaller diameter rear portion, said servo piston being slidable in said smaller diameter rear portion and including at the front end thereof an annular flange slidably fitted in said larger diameter front portion of said cylindrical bore, seal means on said servo piston engaging said smaller diameter rear portion, said annular flange having a number of circumferentially spaced radial notches therein operable to place said high and low oil pressure chambers in fluid communication with each other across the periphery of said servo piston when said servo piston assumes a definite axial position during advancing movement thereof in which said seal means is disengaged from said smaller diameter rear portion and enters said larger diameter front portion.

2. A servo-motor as set forth in claim 1, in which said reaction oil pressure chamber is in fluid communication with said power cylinder through an orifice restricting the rate of pressure oil flow into said reaction oil pressure chamber.

3. A servo-motor as set forth in claim 1, further comprising a relief valve interposed between said low oil pressure chamber and said oil reservoir to maintain said low oil pressure chamber at least at a predetermined level of oil pressure. 

1. An oil-hydraulic servo-motor comprising: a power cylinder having a bore and an output piston slidably fitted in said bore, a control casing secured to said power cylinder at the rear end thereof and defining a cylindrical bore in axial alignment with said power cylinder, a servo piston slidably fitted in said cylindrical bore and defining, when fully retracted, a high and a low oil pressure chamber in said cylindrical bore, respectively, in the front and rear portions thereof, a piston rod extending axially and forwardly from said servo piston and held in sliding engagement with the rear end portion of said power cylinder in end-to-end relation with said output piston, an oil pressure supply source connected to said high oil pressure chamber, an oil reservoir communicating with said low oil pressure chamber, a reaction oil pressure chamber defined in said servo piston and communicating with the bore in said power cylinder, an input piston slidably supported in said control casing in axial alignment with said servo piston and having the piston face thereof extending forwardly into said reaction oil pressure chamber, and control valve means operable in response to limited forward and rearward movement of said input piston to place the bore in said power cylinder in and out of fluid communication with said high and low oil pressure chambers, said cylindrical bore of the control casing having a larger diameter front portion and a smaller diameter rear portion, said servo piston being slidable in said smaller diameter rear portion and including at the front end thereof an annular flange slidably fitted in said larger diameter front portion of said cylindrical bore, seal means on said servo piston engaging said smaller diameter rear portion, said annular flange having a number of circumferentially spaced radial notches therein operable to place said high and low oil pressure chambers in fluid communication with each other across the periphery of said servo piston when said servo piston assumes a definite axial position during advancing movement thereof in which said seal means is disengaged from said smaller diameter rear portion and enters said larger diameter front portion.
 2. A servo-motor as set forth in claim 1, in which said reaction oil pressure chamber is in fluid communication with said power cylinder through an orifice restricting the rate of pressure oil flow into said reaction oil pressuRe chamber.
 3. A servo-motor as set forth in claim 1, further comprising a relief valve interposed between said low oil pressure chamber and said oil reservoir to maintain said low oil pressure chamber at least at a predetermined level of oil pressure. 